1. Field of the Invention
The invention relate to a bearing element comprising a protective layer, a bearing metal layer applied over the protective layer and a sliding layer applied by sputtering over the bearing metal layer, and a method for producing the bearing element.
2. The Prior Art
Technical progress made in the motor industry means that ever increasing demands are made on bearing elements, e.g. sliding bearings. Single layer sliding bearings can no longer satisfy requirements, for example resistance to corrosive wear, due to a layer of oil that thins at high speeds, so that the sliding bearing industry is increasing turning to multiple layer sliding bearings. The latter generally consist of a steel protective coating onto which one or more additional layers are applied by rolling on, plating or sputtering. The additional layers are the bearing metal layer, which if necessary is secured onto the steel protective layer with the insertion of a bonding layer. The sliding layer made from an alloy, for example an aluminium alloy with a higher or lower zinc content or a sliding paint is applied onto said bearing metal layer, if necessary with the interspersion of a bonding layer or diffusion barrier layer.
The intention of these kinds of series of coatings for tribologically stressed components or surfaces is on the one hand to achieve higher ignition pressures for improved thermodynamics and as a result reduced consumption or reduced amounts of exhaust. On the other hand the motor industry now requires lighter engines in addition to increased efficiency, i.e. specific performance, and thereby greater economic savings and greater environmental friendliness of combustion engines, with the result that individual components need to have smaller dimensions. At the same time, in particular at higher temperatures, more dilute lubricating oils need to be used in order to obtain lower frictional power. The required lifetime for motor vehicles, in particular utility vehicles, is at least approx. 1 million kilometres and the intervals between service inspections will also become longer, so that opportunities to inspect sliding elements and their wear are reducing. In other words the average lifetime of a sliding element needs to be increased significantly.
These demands result in a higher specific loading of the sliding elements and higher dynamic stresses. Additionally, smaller lubricating gaps are formed which results in increased and more intensive semi-fluid friction. The result of this can be that boundary friction occurs locally, e.g. on edges, and no bearing lubricant film is formed locally. Owing the reduced dissipation of heat generated by the combustion process local temperature peaks can occur which can damage sliding bearing layers at least in some areas or influence the lifetime of a sliding bearing.